Conventionally, a field emission display is manufactured by vacuum-packaging a lower plate and an upper plate in parallel. The space between the lower plate and the upper plate is within 2 mm. The lower plate includes field emission devices and the upper plate includes phosphors. Electrons are emitted from the field emission devices of the lower plate and the electrons are collided against the phosphors of the upper plate. Right at this time, cathode luminescence effect happens and an image is displayed. Recently, many studies have been performed regarding such field emission displays as a promising flat panel display, replacing conventional cathode ray tube displays.
The key component of field emission display devices is the field emitter and the electron emission efficiency of the field emitter depends upon the structure of the device, the material of the emitter, and the shape of the emitter. The structure of the field emitter can be categorized into diode type and triode type. The diode type includes a cathode and an anode. The triode type includes a cathode, a gate, and an anode. Materials such as metal, silicon, diamond, diamond-like carbon, and carbon nanotube are used as the material of the emitter. Generally, metal or silicon is used to manufacture the triode type and the diamond or carbon nanotube is used for the diode type.
Even though the diode-type field emitters are handicapped by controllability of electron emission and low voltage operation, they are advantageous in some ways. For example, the manufacturing process of the diode-type field emitters is simpler and the reliability of electron emission is higher than the one of the triode-type field emitters.
FIG. 1 shows a diagram illustrating the structure of a conventional field emission display with diode-type field emitters.
Conventional field emission display with diode-type field emitters includes a lower plate 13 with field emitter material and an upper plate 16. The lower plate 13 includes metal electrodes 11 and field emitter material 12 that is filmed on top of the metal electrodes 11. The upper plate 16 includes transparent electrodes 14 and red, green, and blue phosphor 15. With the help of spacer 17, the lower plate 13 and the upper plate 16 are placed in parallel and vacuum-packaged.
In FIG. 1, the metal electrode 11 and the transparent electrode 14 work as a cathode and an anode of field emission devices, respectively. The metal electrode 11 and the transparent electrode 14 are crossed and the crossing section is defined as a pixel.
The conventional field emission display with diode-type field emitters operates as follows.
As shown in FIG. 2, the row signal bus 21R is connected with film-type field emitters 22 in the lower plate 13. Also, as shown in FIG. 3, the column signal bus 31C is connected with the phosphors 32 in the upper plate 16. The row signal bus 21R and the column signal bus 31C can be varied on the basis of the direction of arrangement of the upper plate 16 and the lower plate 13.
The display can be driven in a matrix addressing. The row signal bus 21R selects a row and then the column signal bus 21C carries display signals into the pixels of the selected row. Then, the next row is addressed in the same way, sequentially.
The electric field necessary for the electron emission is determined by a voltage difference between the column signal bus 31C and the row signal bus 21R. When an electric field higher than 1V/.mu.m is leaded to the field emitter material, electron emissions at the field emitter begin.
Unlike cone-shaped triode-type field emitters, diode-type field emitters don't employ insulation film between the gate and the cathode, and therefore the structure and the manufacturing process is simple. In addition, the reliability of the diode-type field emitters is high because the destruction rate of field emitters is very low when electrons are emitted. The destruction of the gate or the gate insulator, which commonly occurs in triode field emitters, rarely occurs in diode-type field emitters.
However, since high voltages have to be loaded at each electrode of the upper plate 16 and the lower plate 13 (the metal electrode of the lower plate 13 and the transparent electrode of the upper plate 16) in field emission displays with diode-type field emitters, high voltage display signals are needed and therefore expensive high-voltage operation circuits are also required. Generally, the space between the electrodes of the upper plate 16 and the lower plate 13 is larger than 200 .mu.m and smaller than 2 mm.
Especially, the anode electrode, the transparent electrode shown in FIG. 1, is used as a display signal bus and an acceleration electrode of electrons at the same time, low voltage operation is almost impossible. That is, since high-energy electrons of more than 200 eV are required to illuminate phosphors in field emission display, a voltage of more than 200V should be biased to the anode electrode. Also, since the structure of diode-type field emitters is thin-film type, the attribute of electron emission is not stable and therefore uniformity is low.
Also, pixels of a conventional field emission display with diode-type field emitters are not electrically isolated each other. Therefore, as the size and resolution of displays increase, the cross-talk of display signals becomes worse.